Glyoxylate transamination

Although the mitochondria are the primary site of oxidation for dietary and storage fats, the peroxisomal oxidation pathway is responsible for the oxidation of very long-chain fatty acids, jS-methyl branched fatty acids, and bile acid precursors. The peroxisomal pathway also plays a role in the oxidation of dicarboxylic acids. In addition, it plays a role in isoprenoid biosynthesis and amino acid metabolism. Peroxisomes are also involved in bile acid biosynthesis, a part of plasmalogen synthesis and glyoxylate transamination. Furthermore, the literature indicates that peroxisomes participate in cholesterol biosynthesis, hydrogen peroxide-based cellular respiration, purine, fatty acid, long-chain... 

Glyoxysomes do not contain all the enzymes needed to run the glyoxylate cycle succinate dehydrogenase, fumarase, and malate dehydrogenase are absent. Consequently, glyoxysomes must cooperate with mitochondria to run their cycle (Figure 20.31). Succinate travels from the glyoxysomes to the mitochondria, where it is converted to oxaloacetate. Transamination to aspartate follows... 

This pyridoxal 5-phosphate-dependent enzyme [EC 2.6.1.4] catalyzes the transamination of glyoxylate from L-glutamate to produce glycine and a-ketoglutarate. 

Located in the peroxisomes of liver, L-alanine-glyoxylate aminotransferase catalyzes the transamination of alanine and glyoxylate to form pyruvate and glycine. A rare inborn error of metabolism manifested as hyperoxaluria is due to a deficiency of this enzyme. 

Salvage operation. Write a balanced equation for the transamination of glyoxylate to yield glycine. 

Glycine (aminoacetic acid, aminoethanoic acid) is HjN. CHj.COOH, with = 2.4. It is transaminated by an ala-nine-glyoxylate aminotransferase. The glycine can then be incorporated into proteins and used for serine synthesis or simply be degraded. 

Althongh glyoxalate can be transaminated back to glycine, this is not really considered a biosynthetic ronte for new glycine, becanse the primary ronte for glyoxylate formation is from glycine oxidation. 

The enzyme aspartate decarboxylase (EC 4.1.1.11) will decarboxylate aminomalonic acid in H20 to yield (25)-[2- HJglycine and will also transaminate glyoxylic acid in H20 to yield (2K)-[2- H]]glycine (78). The chirality of the product was assayed using the pro-S specific D-amino acid oxidase (EC 1.4.3.3). 

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